Article Pleistocene Bryozoans from the Clyde Clay Formation of Scotland, and the Holocene Retreat of Cold-Water Species Paul David Taylor Department of Earth Sciences, Natural History Museum, London SW7 5BD, UK; [email protected] Abstract: Although bryozoans are a diverse phylum of aquatic invertebrates with a rich fossil record, very little has been written about bryozoan faunas from the latest Pleistocene at a time of rapid global change when temperatures increased dramatically and the sea-level rose. Two species of cyclostome and eight species of cheilostome bryozoans are here described from the late Devensian Clyde Clay Formation of Greenock, Scotland, based on historical material in the collections of the NHM, UK. All are illustrated for the first time from this deposit using scanning electron microscopy. Three of the species (Tubulipora cf. marisalbi, Rhamphostomella radiatula and Schizomavella porifera) are unknown from the seas around Scotland at the present-day but occur in colder waters to the north. This is consistent with the poleward retreat of cold-water species as seawater temperatures increased at the end of the Pleistocene. Keywords: Bryozoa; Pleistocene; Scotland; biogeography; global warming 1. Introduction Citation: Taylor, P.D. Pleistocene Bryozoans from the Clyde Clay Concomitant with global warming and facilitated by human-related dispersal mecha- Formation of Scotland, and the nisms, the last few decades have seen the expansion of the ranges of several bryozoan species Holocene Retreat of Cold-Water into higher latitudes. These include warm-water fouling species, notably Bugula neritina, Species. Taxonomy 2021, 1, 69–82. Watersipora subatra and Schizoporella japonica, which have begun to appear in harbours increas- https://doi.org/10.3390/taxonomy ingly further north in the Atlantic waters of northwest Europe [1–3]. A further expectation 1020008 is that the ranges of cold-water bryozoan species will have contracted polewards as sea temperatures increased, causing local extinctions. However, it is unclear whether any such Academic Editor: Marco Taviani range contractions have actually been documented. Rapid climatic warming marked the end of the so-called Ice Age in the late Pleis- Received: 9 April 2021 tocene [4]. Comparing the composition of fossil bryozoan faunas formed at this time with Accepted: 25 April 2021 those of the present-day in the same region has the potential for identifying local extinctions Published: 6 May 2021 of cold-adapted species. Unfortunately, very little has been published on bryozoans from the latest Pleistocene, especially in northern Europe. The presence in the Natural History Publisher’s Note: MDPI stays neutral Museum, London (NHMUK) of some latest Pleistocene bryozoans collected during the late with regard to jurisdictional claims in 19th century from temporary exposures near the shore of the Firth of Clyde downstream of published maps and institutional affil- Glasgow at Garvel Park, Greenock (Figure1), allows a glimpse of a bryozoan fauna that iations. lived at a coastal site following deglaciation and sea-level rise. A few lists of bryozoan species from the Garvel Park have been published [5–7], but none of the species recorded have been described or figured. The current paper provides the first descriptions and fig- ures of the Garvel Park bryozoans, some of which no longer live in Scottish waters but are Copyright: © 2021 by the author. present in colder waters further to the north, an example of ‘trailing-edge extirpation’ [8]. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Taxonomy 2021, 1, 69–82. https://doi.org/10.3390/taxonomy1020008 https://www.mdpi.com/journal/taxonomy TaxonomyTaxonomy 20212021, 1,1 FOR PEER REVIEW 2 , 70 Figure 1. Regions of the sea around Scotland, based on work by Rouse and others [9], and the Figurelocation 1. Regions (star) of of the the latest sea around Pleistocene Scotland, fossil based bryozoan on work locality by atRouse Garvel and Park, others Greenock. [9], and the loca- tion (star) of the latest Pleistocene fossil bryozoan locality at Garvel Park, Greenock. 2. Materials and Methods 2. MaterialsThis taxonomicand Methods study is based entirely on historical material lodged in the fossil collectionsThis taxonomic of the NHMUK. study is based Some ofentirely these specimenson historical were material presented lodged to thein the museum fossil col- by D. Robertson on 4 November 1883, one is from the collection of J. Young and a few are from lections of the NHMUK. Some of these specimens were presented to the museum by D. the collection of E. Jelly, who is known to have received bryozoans from other collectors Robertson on 4 November 1883, one is from the collection of J. Young and a few are from and then redistributed them to her colleagues. The specimens donated by Robertson are the collection of E. Jelly, who is known to have received bryozoans from other collectors labelled ‘Garvel Park, Greenock’. Other specimens, which were apparently collected at and then redistributed them to her colleagues. The specimens donated by Robertson are about the same time, probably came from the same locality or very nearby. Colonies are labelled ‘Garvel Park, Greenock’. Other specimens, which were apparently collected at fragmentary but well preserved, allowing identification to species level in most instances. about the same time, probably came from the same locality or very nearby. Colonies are Robertson [6] gave a detailed account of the Pleistocene geology of Garvel Park, fragmentary but well preserved, allowing identification to species level in most instances. Greenock, where the construction of a dry dock in 1870 and a wet dock in 1881 exposed Robertson [6] gave a detailed account of the Pleistocene geology of Garvel Park, boulder clay overlain by a sequence of clays and sands containing marine shells. These Greenock, where the construction of a dry dock in 1870 and a wet dock in 1881 exposed late glacial marine deposits came to become known as the ‘Clyde beds’ [10] or ‘Garvel boulderPark Beds’ clay [overlain7] but have by a since sequence been givenof clay thes and formal sands name containing Clyde Clay marine Formation shells. These [11,12 ]. lateNo glacial permanent marine exposures deposits existcame at to Greenock become known but temporary as the ‘Clyde excavations beds’ [10] both or during ‘Garvel the Parklate Beds’ 19th century[7] but have and since again been in 1962 given allowed the formal the Clyde name Clay Clyde Fm. Clay to Formation be seen in six[11,12]. small Nobasins permanent to a thickness exposures of 10exist m orat moreGreenock [10]. but Unfortunately, temporary excavations the exact stratigraphical both during levelthe late(or 19th levels) century from whichand again the bryozoansin 1962 allowed were collected the Clyde is unknown.Clay Fm. to The be Clyde seen in Clay six Fm.small is a basinsglaciomarine to a thickness deposit of considered10 m or more to have[10]. beenUnfortunately, formed during the exac thet latestratigraphical Devensian (=level late (orWeichselian) levels) from Marine which the Isotope bryozoans Stage2, were about collected 13–10 ka is BPunknown. [12,13]. The Clyde Clay Fm. is a glaciomarineAfter initial deposit study considered with an to optical have been microscope, formed theduring bryozoans the late were Devensian examined (= late and Weichselian)imaged using Marine a LEO Isotope 1455-VP Stage scanning 2, about electron 13–10 microscope. ka BP [12,13]. This instrument was operated in lowAfter vacuum initial mode,study with allowing an optical the uncoated microscope, bryozoans the bryozoans to be imaged were using examined a back-scattered and im- agedelectron using detector. a LEO 1455-VP Species scanning descriptions electron are basedmicroscope. on the This scanning instrument electron was micrographs operated inobtained, low vacuum and mode, measurements allowing were the uncoated made from bryozoans these calibrated to be imaged micrographs. using aAbbreviated back-scat- Taxonomy 2021, 1, FOR PEER REVIEW 3 Taxonomy 2021, 1 71 tered electron detector. Species descriptions are based on the scanning electron micro- graphs obtained, and measurements were made from these calibrated micrographs. Ab- breviated synonymies are given for each species that include the first description, first synonymiesreferral to the are currently given for accepted each species genus, that and include a modern the first description. description, first referral to the currently accepted genus, and a modern description. 3. Results 3. Results 3.1. Systematics 3.1. Systematics Phylum Bryozoa Ehrenberg, 1831 Phylum Bryozoa Ehrenberg, 1831 Class Stenolaemata Borg, 1926 Class Stenolaemata Borg, 1926 Order Cyclostomata Busk, 1852 Order Cyclostomata Busk, 1852 3.1.1. Family Tubuliporidae Johnston, 1837 3.1.1. Family Tubuliporidae Johnston, 1837 Genus Tubulipora Lamarck, 1816 Genus Tubulipora Lamarck, 1816 Tubulipora cf. marisalbi Gostilovskaja, 1955 Tubulipora cf. marisalbi Gostilovskaja, 1955 FigureFigure2 2A–CA–C FigureFigure 2.2. Cyclostome bryozoans bryozoans from from the the Clyde Clyde Clay Clay Formation Formation of of Garvel Garvel Park, Park, Greenock, Greenock, Scot- Scot- land.land. ( (AA––CC)) TubuliporaTubulipora cf.cf. marisalbimarisalbi Gostilovskaja,Gostilovskaja, 1955, 1955, NHMUK NHMUK B1223e; B1223e; (A) entire (A) entire specimen;